<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
</head>
<body>
    <div id="app">
       <div class="input-num"></div>
       <button @click="sub">-</button>
       <span>{{ num }}</span>
       <button @click="add">+</button>
      </div>

      <script>
          var app = new Vue({
        el: '#app',
        data: {
            num:1
        },
        methods:{
            add:function(){
                if(this.num<10){
                    this.num++;
                }else{
                    alert("已经到头了");
                }
            },
            sub:function(){
                if(this.num>0){
                    this.num--;
                }else{
                    alert("已经到头了");
                }
            }
        }
      })
      </script>
      
</body>
</html>